Self-excited alternator.



imamuf PATBNTBD MAR.10, 1908.

E. P. W. .ALBXANDERS0N.

SELF EXCITBD ALTERNATOR.

APPLLOATION HLED FEB.19.1906.

Cil

. circuited secondary, and .consequently the e ANDERSON, a subject of the King of Sweden,

-ments in Self-Excited Alternators, of which .and in series, respectively. A convenient `method of obtaining they shunt excitation isv winding' is that disclosed `in my former Yactance of the auxiliary winding, and consists m su `plying a short-cireuited winding ving its self-induction.

UNITED STATES Pig-TENT-onnion.

ERNST F. W. ALXANDERSON, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRICVCOMPAN Y, A CORPORATION OF NEW YORK.

sELF-Excrrnn LTERNATOR.

i Specification of Letters Patent.

Patented March 1o, loos.

Tot all' whom. may concern: i y Be a imam that i, ERNST F. w. ALEXn i residing at"Schenectady, in the. county oi Schenectady and State'of Yew-York, have invented certain new and useful Improve-I the follow'vingis a specication. v

. My invention relates to self-excitingy al-v ternators,l and lis particularly aplicable to the type of machine described in atent No. 789,476, issued to me May 9, 1905. In that patent I disclosed a self-'exciting alternating-y ycurrent machine having a Afield winding provided wit'h afrectifying commutator and means for supplying tothe field winding 'through the commutator'super-posed voltages, .derived-from the armature in shunt' through an auxiliary winding carried by the armature, and by means of thisv arrangement the expense of shunt transformers is saved. One suitable arrangement for the auxiliary Patent No. y849,713,issuedApril 9, 1'907, in which. the auxiliary winding. is composed of conducting strips which are inserted m the armature slots between the armature coilsr and the retaining wedges. This arrangement of. the auxiliary winding at the top of the slot'gives the winding the minimum re- Ny, present invention comprises an additional feature for further reducing the retothe-fiel y I'nagnet'in inductive relation tov the' auxiliary. winding. This short-circuited Winding actsvas al low-resistance secondary for the auxiliary winding, materially lower- My invention is articularly advantageous in connection witi machines having laminated lield magnets, since in such machinesv the field magnet itself cannot act as a shortreactance of the auxiliary winding is high.

My invention is also .particularly adapted for use in machines of the type having cylindrical field magnets such as are ordinarily employed in turbine-driven machines -at the present time` Field magnets of this type .are shown diagrammatically.

offer a path of low reluctance for the flux from a coil lin the armature, which tends "to increase the reluctance ofthe auxiliary winding. This tendency is overcome by means of my invention.

ln the accompanying drawings, Figure 1 shows an end-view, partly 1n crossfsection,

of a self-exciting alternator arranged in accordance with my invention and Fig. 2 is a diagram of the circuit connections.

In the drawings, A vrepresents the armature core which is built up of laminations in the usual manner.

A .represents thel main armature coils which are carried in slots and held. in place by suitable retaining wedges.

a; represents the auxiliary Winding, which is inserted inthe armature slots between the armature Winding and the retaining means, as described in my former application above. referred to. These strips `are placed in as many slots as necessary to give the desired voltage, and the strips are connected to give 'a winding lany desired character.

i F represents the field magnet, which is shown as of the cylindrical ,typey commonly employed in turbine-,driven alternators.

"F represents the field coils carried in slots in the field magnet. The eld magnet is also provi-ded with a'vsho'rtcircuited distributed winding f in inductive relation to the auxiliary Winding so asv to vact as a shortcircuited secondary to lreduce the reactance of the auxiliary Winding. As shown in the drawing this short-.circuited winding may be formed convenientlybyr` shortcircuiting a few of the turns of the 'field coils and winding some of theseshort-circuited turns around the portions of the field magnet between'thepoles. @represents a rectifying commutator, to the segments oi' which t-he terminals of the lieldwinding F are`connected.

b represents brushes .bearing on the commutator, and connected. to the auxiliaryy winding. Through these brushes and through the rectifying commutator the exciting cur-` rent is supplied from the auxiliary winding to the field. g

ln Fig. 2 the connections of the machine These oonnections are fully explained in my former patents above referred to, but will be briefly mature .vinding.

This commutator is'of the type disclosed in my fornierpatents, comprising a polyphase arrangement of brushes b b and se ments of a length substantially equal to the istance be. i

tween brushes. As fully explained in my former patents, if a polyphase voltage is iiniessed upon the brushes a rectified current is delivered to the ,field Winding. The arrangement of brushes shown is adapted for a tlireepliase excitation, and the auxiliary Winding a is consequently arranged and connected in three-phase. The resistances 1" are placed in series With the several hases of the auxiliary Winding, and .across t e terminals of these resfstances are connected the secondaries of transformers, T T, the prima'- ries or which are in series ivith the main-ar- These transformers serve to impress across the terminals of the resistancesr in series with the auxiliary Winding voltages corresponding in amount and phase to the armature current. These transformers are so connected to the resistances that the phase of the voltage impressed across the terminals of the resistances r is ninety .degrees from the phase of the voltage of the auxiliary winding When the load on the niachine is non-inductive. This arrangement, as fully explained in in'y former patents, giv'es proper compounding for both inductive and non-inductive loads. R represents a field rlieostat by means of which the voltage of. the machine may be regulated in the usual manner. v

It will be seen that as the field magnet and its rectifying comniutator revolve, the circuits of the several phases of the exciting Winding are successively broken. In order to avoid sparking due to this breakiiigof its circuit, the auxiliary Winding should have as lou a reactance as ossible, and since the short-circuited Winding on the field above g described assists 'in producing a low reactance, it 1s of assistance' in producing perfect commutation.

What I claiin as new and desire to secure said tor and connected to said aureiliary winding, i

and a short-circuited winding carried by the field magnet. in inductive relation to said auxiliary winding.

2. ,In a self-exciting alternator, a slotted armature core, a main armature Winding in 1 said sletsfan auxiliary winding 1n the top'of said slcts-above the .armature winding, la field magnet,a field winding carried thereby )rovided ,with a rectifying c'oinni'utator,l brushes bearing on said commutator and connected to said auxiliary winding, anda short-circuited winding carriedby the field magnet in inductive relation to said auxiliary' Winding.

3. In a self-exciting alternator, a main armature Winding, an auxiliary winding, a field magnet, a field Windingcarried thereby provided with a rectifying coinniutator, and brushes bearing on said coinmutator and connected to said auxiliary Winding, said field Winding'having a fen7 t'uriis short-circuited on themselves.

4. In a self-exciting alternator, a main. armature winding, an auxiliary winding, a field magnet, a field winding carried thereby `)rovided with a rectifying coniinutator, brushes bearingon said commutator and connected to' said auxiliary winding, and shortcircui'ted Vconductors surrounding each pole and the spaces `between poles.

5. In a self-exciting alternator, a main armature Winding, an auxiliary winding, a cylindrical field magnet, a field winding carried in. slots therein and provided with a rectifying coinmutator, brushes bearing on said coniniutator and connected to said auxiliary winding, and short-circuited conductors surrounding each field pole and the spaces betweenI poles.

6. In a self-exciting alternator, r main armature winding, an auxiliary Winding, a cylindrical field'iiiagnet, a field Winding carried in slots therein and provided with-a rectifying coinniutator, brushes bearing on said cominutator and connected to said auxiliary Winding, said field Winding having a few turns short-circuited on themselves and a portion of said turns being arranged to surround the spaces between poles..-

v7. In a self-exciting alternator, a main armature Winding.' an auxiliary winding, a cylindrical field magnet, a field Windingcarried in slots vtherein and provided with a rectifying conuiiutator, brushes bearing on coiumutator andconnected to said auxiliary Winding, and sliort-circuited conductors in the top of the field magnet slots surrounding each field pole and the spaces between poles.

In witness whereof', I have hereunto set my hand thisl .l 7th dav of February, '1906.

ERNST F. W. ALEXXDERSUN.

Witnesses:

BENJAMIN B. HULL, HELEN OnFoRD. 

